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SAY AHHH, FOR COMPOSITE RESIN FILERS: A STUDY OF THE COMPOSITE RESIN by Vishal Patel A Thesis in Chemistry Education Presented to the Faculty of the University of Pennsylvania in partial fulfillment of the requirement of the Degree of Master of Chemistry Education At University of Pennsylvania 2007 __________________________________________________ Constance W. Blasie Program Director __________________________________________________ Dr. Andrew Rappe Supervisor of Thesis __________________________________________________

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Page 1: SAY AHHH, FOR COMPOSITE RESIN FILERS: A STUDY OF THE ...vishalpa/Thesis makes you go to sleep.pdf · SAY AHHH, FOR COMPOSITE RESIN FILERS: A STUDY OF THE COMPOSITE RESIN by Vishal

SAY AHHH, FOR COMPOSITE RESIN FILERS: A STUDY OF THE COMPOSITE RESIN

by

Vishal Patel

A Thesis in Chemistry Education

Presented to the Faculty of the University of Pennsylvania in partial fulfillment of the

requirement of the Degree of

Master of Chemistry Education

At

University of Pennsylvania

2007

__________________________________________________

Constance W. Blasie Program Director

__________________________________________________

Dr. Andrew Rappe Supervisor of Thesis

__________________________________________________

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University of Pennsylvania

Abstract

SAY AHHH, FOR COMPOSITE RESIN FILERS: A STUDY OF THE COMPOSITE RESIN

by Vishal Patel

Chairperson of the Supervisory Committee: Professor Dr. Andrew Rappe Department of Science

Abstract – Caries are an infectious disease which can be prevented by practicing proper dental hygiene. In order to understand how caries develop it is important to understand the anatomical structure and function of enamel, dentin, and pulp. The process of demineralization of the enamel layer occurs due to the break down of sucrose which is a common sugar ingested daily. The sucrose is hydrolyzed to produce glucose and fructose. Fructose is broken down via multiple steps of glycolysis to produce lactic acid and a hydrogen ion which dissolves the enamel layer. Once the enamel is demineralized, caries begin to develop. Caries need to be treated with a proper filling which can hold up for multiple years to prevent the caries to further decompose the tooth or even possibly fracture a tooth. Amalgam has been used for many years and due to its appearance in the mouth, composite resins are being considered as an alternative. The most common dental composite resin currently used is bis-GMA; however, its high viscosity and shrinkage concerns have forced alternative composite resins to be researched. A cube structure known as silsesquioxanes have been used with organic tethers which are used to crosslink the cube structures. The crosslinking of the hard core composite resin matrix with the organic, soft tethers allow the cubes to readjust even after the initial reaction. The silsesquioxanes are one of many alternatives being reconsidered.

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TABLE OF CONTENTS

List of Figures.......................................................................................................................ii List of Tables .......................................................................................................................iii Preface.................................................................................................................................. iv Anatomy of tooth ................................................................................................................1 Formation of Carries (Cavities).........................................................................................1 Amalgam Fillings .................................................................................................................3 Composite Resins and Cements .......................................................................................7

Text Box #1 (What’s free about free radicals?) ................................................... 10 Text Box #2 (Concreteness of Cement) .............................................................. 13 Post Shrinkage................................................................................................................... 17 State of the Art Composite Resin.................................................................................. 18 Conclusion ......................................................................................................................... 22 Bibliography....................................................................................................................... 24 Appendix A: Lesson Overview...................................................................................... 26

Lesson Plan (Day 1) .................................................................................................. 29 Experiment 1.............................................................................................................. 33 Experiment 2.............................................................................................................. 39 Experiment 3.............................................................................................................. 44 Lesson Plan (Day 2) .................................................................................................. 49 Lesson Plan (Day 3) .................................................................................................. 53 Daily Learning Log.................................................................................................... 58 PIM............................................................................................................................... 59

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LIST OF FIGURES

Number Page 1) Tooth Anatomy........................................................................................................1

2) Steps to tooth decay ................................................................................................1

3) Demineralization of Enamel..................................................................................2

4) Sucrose .......................................................................................................................2

5) Hydrolysis..................................................................................................................2

6) Glycolysis...................................................................................................................3

7) Formation of Lactic Acid .......................................................................................3

8) Restored and repaired amalgam restoration .......................................................4

9) Elements used to make amalgam..........................................................................4

10) Symbols and Stoichiometry .................................................................................4

11) Silver-tin phase diagram........................................................................................5

12) Disposal Amalgam vial ........................................................................................5

13) General amalgamation reaction .........................................................................5

14) Schematic drawing of amalgam microstructure ..............................................6

15) Mechanics of Amalgam filling.............................................................................6

16) Amalgam photomicrograph.................................................................................6

17) Human Mercury Exposure ..................................................................................7

18) γ-methacryloxypropyltrimethoxysilane..............................................................8

19) 2-methyl-2-Propenoic acid (1-methylethylidene) bis (4,1-phenylenoxy-2-Hydroxy-3,1-

Propanediyl)) (Bis-GMA).....................................................................................8

20) Stick model of bis-GMA .....................................................................................8

21) Ball and stick model of bis-GMA.......................................................................8

22) Amino-carboxylate based bonding agent (NPG-GMA) ...............................9

23) Carboxylate-based bonding agent.......................................................................9

24) Phosphate based bonding agent ........................................................................9

25) Camphorquinone................................................................................................ 10

26) Light-curing process .......................................................................................... 10

27) Heterolytic Cleavage........................................................................................... 10

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28) Homolytic Bond Cleavage ............................................................................... 11

29) Benzoyl Peroxide ................................................................................................ 11

30) Initiation .............................................................................................................. 11

31) Electromagnetic Spectrum................................................................................ 12

32) Propagation Stage .............................................................................................. 12

33) Chain Transfer..................................................................................................... 12

34) Second type of chain transfer ........................................................................... 13

35) Termination ......................................................................................................... 13

36) Cement Factory................................................................................................... 14

37) Cement Hydration .............................................................................................. 14

38) Organic Monomers ............................................................................................ 16

39) Ball and stick model of ethylene glycol dimethacrylate (EGDMA).......... 16

40) Ball and stick model of triethylene glycol dimethacrylate (TEGDMA)... 16

41) Composition of dental cements ....................................................................... 16

42) Termination highlighting the unreacted double bonds ............................... 17

43) Monomer composition...................................................................................... 17

44) Content of CQ ................................................................................................... 17

45) Microscopic image of prosthesis .................................................................... 18

46) Typical size and volume of cube..................................................................... 18

47) Example of tether.............................................................................................. 19

48) Example of tether.............................................................................................. 19

49) Example of tether.............................................................................................. 19

50) Example of tether.............................................................................................. 19

51) Example of tether.............................................................................................. 19

52) Example of tether............................................................................................. 19

53) Continuous organic phase................................................................................ 19

54) Non-continuous phase ..................................................................................... 19

55) Process of how crosslinking occurs ............................................................... 20

56) DDM alters nanocomposite............................................................................ 20

57) Formation of nanocomposite ......................................................................... 21

58) Change of setting shrinkage of composite resin.......................................... 21

59) Monomers used in Okamura’s study ............................................................. 22

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ACKNOWLEDGMENTS

I would like to express sincere appreciation to all of the administrators, faculty and especially Professor Andrew Rappe for his assistance in the preparation of this manuscript. In addition, special thanks to Megan Cubbage whose familiarity with the needs and ideas of the class was helpful during the early planning phase of this undertaking.

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Anatomy of tooth We always manage to understand by means of research how our world, the things which are in our environment and most importantly how our bodies work to best explain to each other and ourselves what is happening chemically. Chemists and material scientists have conducted research to allow something as small as a cavity in your mouth to be filled with some sort of material, which is referred to as a composite, resin, and/or dental fillers in the dental profession. Cement is a non-metallic substance which hardens to act as a base, liner, filler, material, or adhesive to bind devices and prostheses to tooth structure or to each other. 1, 2 A composite is a solid formed from two or more phases that have been combined to produce properties superior to or intermediate to those of the individual constituents. Fillers are best described as a combination of organic and inorganic resin particles that are designed to strengthen a composite, decrease thermal expansion minimize polymerization shrinkage and reduce the amount of swelling caused by water sorption. Not being satisfied with the quality of materials currently being used, scientist are hard at work attempting to find better materials which can be used to fill voids in teeth. This research paper briefly explains the various materials used to fill caries (cavities), chemically examines a popular monomer used in the dental profession and current research being conducted to bring about new changes in the process of treating caries. To best understand how cavities form, the anatomy of the tooth needs to be understood. Refer to the figure 1.3

Figure 1: Tooth anatomy3 The anatomical structures relevant to having a clear understanding of this paper are the dentin, pulp and enamel. The function of dentin is to act as a mechanical buffer between dead and living substances, and thus, between mechanical hard and soft material. Pulp is the vital layer of the tooth which delivers needed nutrients and blood supply to the tooth for growth and development.4 The enamel is the primary armor of the tooth. It is one of the hardest biological substances is the enamel. Enamel has hardness greater than that of bones. The Knoop Hardness Number assigned to enamel is in the range of 340 to 431 kg/mm2.2 Enamel is entirely composed of calcium salts which are important in composite bonding process. Formation of Caries (cavities)

Figure 2: Steps to tooth decay.5

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The figure above shows the tooth decay process from absolute healthy tooth to a fracture. The first tooth is a health tooth. The second tooth shows the first sign of demineralization of the enamel layer. The third tooth shows the results of enamel breakdown. The forth tooth has had an amalgam filler applied to it; however, the demineralization of the enamel has not been addressed which are visible in the fifth tooth and leading to a fracture. Had the demineralization been address the tooth could have been saved from further decay. The mechanism which causes the demineralization of the enamel layer is shown below.

Figure 3: Demineralization of Enamel

It is at the surface of the tooth or the enamel which is the hardest and most mineralized substance in the body and where the formations of caries occur. Caries are an infectious disease that destroys the tooth which is caused by bacteria and carbohydrate containing foods.6 Bacteria forms on and around teeth in the form of a thin bio-film known as plaque which is made up of millions of bacteria which adhere to the tooth’s surface. Not all bacteria contribute to the formation of teeth caries. Streptococcus mutants, lactobacillus casei, acidophilus and actinomyces naeslunddii are the common carie causing bacteria.7 These bacteria seek carbohydrates to survive and produce acid in the mouth. After eating sugary foods and after brushing your teeth, glycoproteins which are a combination of proteins and carbohydrate attach to teeth surface where plaque begins to build. While the plaque is forming, streptococci are hard at work forming

carries. The figures below8 show the formation of the lactic acid. This is the acid which causes the pH on the tooth’s surface to drop. Before the intake of any foods, the pH level in the mouth is slightly more acidic than water, (6.2 – 7.0).9 When the pH range is between 5.2-5.5, the enamel begins to be dissolved and the exposure of these foods promotes an acid attack of approximately twenty minutes after eating. The millions of bacteria that reside on the surface of the teeth ferment the sugar we intake to form lactic acid which in-turn attacks the enamel. The demineralization of the enamel is actually caused by the hydrogen ion produced by the lactic acid.

Figure 4: Sucrose8

Figure 5: Hydrolysis of Sucrose8

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Figure 6: Glycolysis

Figure 7: Formation of Lactic Acid8

The two ways in which caries develop are trough pits and fissures which are grooves that are visible on the top biting surfaces of the back teeth. This occurs when food becomes trapped in pits and over time plaque forms a carie. The carie begins to form at one point and spreads to the dentin. The second method of cavity formation is acid attack on the tooth’s surface. Over a long time exposure of the acid to the enamel

surface breaks down the enamel and the acid destroys the layer. Once a carie has formed, it is the dentist’s job to clean and apply filler to it. There are two categories of fillings which are direct restorations (amalgam, composites, glass ionomers and resin ionomers), and indirect restorations (all porcelain (ceramic), porcelain fused to metal, gold alloy (high noble) base metal alloys (non-noble). Due to cost of the material involved, direct restorations are the more common of the two types. Direct fillings can be subcategorized into silver amalgam, composite, and temporary filling materials. Amalgam Fillings

Amalgam restorations have been used for 180 years.10 Amalgam fillings are the hardest type of filler currently being used. Knoop Hardness Number of 901 has been assigned to amalgam. Recent research indicates that amalgam restorations have a tendency to last longer than previously estimated. The dental hygiene practiced by the individual has a great effect on how long and how well amalgam fillers hold up. The

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low concentration of amalgam (before 1963)11, caused the amalgam to weaken via corrosion because they contained gamma 2 phase (Ag3Sn), as shown in figure 11.2

Figure 8: Restored and repaired amalgam restoration.11 (The American National Standards Institute (ANSI) along with the American Dental Association (ADA) requires that amalgam alloys are mainly comprised of silver and tin.2

Figure 9: Elements used to make amalgam.1 The specific amounts of elements are not exactly mandated which is seen by comparing figure 9 and the following. Amalgam is comprised of mercury, and alloy power containing 40 to 70% of silver, 12 to 30% tin, 12 to 30% copper, 1% zinc and either 0.5% of palladium or indium10, 11.

Zinc is incorporated into the amalgam to improve its clinical performance.12-14 Dental amalgam with mercury are described by the metallurgical phases (silver-tin phase diagram)52.

Figure 10: Symbols and Stoichiometry of Phases that are Involved in Setting of Dental Amalgams are referred to the mixture of the two metallic elements by a Greek letter.2 The Greek letters correspond to the symbols found in the phase diagram for each alloy system1. Amalgam fillings are extremely durable, long lasting and not likely to break. Amalgams have been known withstand multiple years of chewing stress. The silver-tin phase diagram indicates that when an alloy contains 27% tin (Sn). Tin is cooled below 480oC, Ag3Sn the gamma phase in the diagram is produced. Silver-tin compound is a key compound in this specific amalgam which combines with mercury to obtain the properties and characteristics sought. The silver-tin compound forms over a very narrow composition range. The silver content for silver-tin amalgam is 73%, the tin content is approximately 26% and 30% of the remaining elements used for the silver-tin amalgam are silver, copper, and zinc. If the tin concentration is less than 26%, the β phase which is a solid solution of silver and tin forms. Different varieties of amalgam are obtained by slightly altering the amount (percentage concentration) of tin or palladium. In one type of amalgam 5% indium is replaced by 5% of tin and in another type contains <1% palladium. Corrosion resistance and mechanical

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properties are enhanced by the addition of palladium in amalgams .

Figure 11: Silver-tin phase diagram2 (λ is also referred to as Ag3Sn. β is the solid solution of silver and tin. ) Amalgation (the process of mixing liquid mercury with one or more metals or alloys to form an amalgam) occurs when mercury contains the surface of the silver-tin alloy particles. The various other elements (copper, zinc, gold, mercury, palladium, indium and selenium)1 are not exactly specified; however they must be in concentrations less than the concentrations of tin and silver.

Figure 12: Disposal Amalgam vial.

Amalgam is made available to dentists in a disposable vial as shown above. The mercury is kept separate from the powdered particles and the mixing pellet by a thin film. The amalgam is prepared by a method referred to as trituration (mixing of mercury with the powder particles). When the amalgam is triturated it has the consistency similar to that of a paste. When the triturated amalgam is removed from the vial it may be further worked by the dentist using a spatula. The dentist is required to mold the surface of the amalgam filling to reduce the tensile stress caused by biting forces. Amalgams are self sealing, when amalgam is applied to the tooth, corrosion occurs which fills microscopic voids between tooth and filling.

Figure 13: The general amalgamation reaction. (λ2 is also referred to as Sn7-8Hg. λ is also referred to as Ag3Sn. β is the solid solution of silver and tin. ) The physical properties of the hardened amalgam depend on the concentrations of each microstructural phase. If the percentage composition of tin is >30% or <26% it is detrimental to the amalgam. The source of amalgam’s strength is due to the Ag3Sn rather then the tin. The setting time or the amount of time required to fill the carie is shortened by increasing the silver content. Creep resistance is also better when Ag3Sn is used rather than amalgam with a higher tin content

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Figure 14: A-D are schematic drawings illustrating the sequence of development of amalgam microstructure when lathe-cut low-copper alloy particles are mixed with mercury. (A) Dissolution of silver and tin into mercury. (B) Precipitation of γ1 crystals in the mercury. (C) Consumption of the remaining mercury by growth of γ1 and γ2 particles. (D) Amalgam when finally set.2

The bond strengths have been reviewed in many clinical studies which indicate they are about 12 to 15 megapascals (MPa).11 Summitt’s group has reported an average bond strength of 27 MPa.15 The larger bond strength was reached by refrigeration of the bonding material is the appointed source which can be the source of the unusual bond strength of 27 MPa. Bonding is emphasized with amalgams because it offers sealing properties which is the primary deter to microleackage. Acid etching of tooth’s surface is done with phosphoric acid in various concentrations to deter microleackage.

Figure 15: Mechanism of bonding amalgam to tooth structure.1

Figure 16: Scanning electron photomicrograph of interface between bonding agent and dental amalgam.1 The two important properties that a are very closely related to the behavior of alloys are high compressive strength and low creep (time dependent strain or deformation that has produced some external source of stress1). Studies have indicated that creep is directly linked to low-cooper amalgams. Creep is reported by the

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degree of marginal deterioration, hence the higher the creep magnitude, the greater the degree of marginal deterioration.16 As reported by Mahler and group17 the two major factors of corrosion and creep are the determinants of the amalgam behavior which are best explained by the final concentration of mercury. The higher the concentration of mercury in an amalgam increases the possibility of the creep. Creep is not a good predictor of marginal fracture. As you can clearly see in figure 5, the amalgam fillings are easily identifiable in one’s mouth. In clinical practice, healthy tooth must be removed to allocate the needed space for the amalgam filling to hold it securely in place. Amalgam fillings can corrode over time which may lead to slight discoloration of the area of contact to the amalgam. Traditional amalgam fillings do not necessarily bond to teeth but rather sit in the enlarged cavity which explains the reason of why healthy tooth is required to be removed. Sometimes people may be allergic to mercury or be concerned about its effects. The mercury in amalgam has a very small tendency to vaporize when chewing of food especially hard foods occurs. Research supports the amount of mercury exposed from fillings is comparable to what people get from other sources in the environment.18 To address these concerns alternative filling are also available for slightly higher cost and require a lengthier setting time.

Figure 17: Estimated human mercury exposure reported in 1991.18 Composites Resins and Cements Composite resins are a mixture of plastic and fine glass particles and are generally applicable for small and large fillings for front teeth or the visible parts of teeth & now by popular demands rear teeth. Composite resin tends to hold up for approximately five years. Composite fillings or inlays are not noticeable since they can be matched to the tooth color selected by the dentist. Such a filling can be completed in one visit and an inlay may require two visits to complete. Composite fillings bond directly to the tooth via ionic bonding which makes the tooth structurally stronger than the amalgam which is a filling pushed into the carie. Less drilling is involved with the composite fillings because it is not necessary to create space to hold the filling securely. The bonding process holds the composite resin in the tooth. Often times indirect composite resin can are combined with glass ionomers to provide the benefits of the two materials. Composites are highly cross-linked polymeric materials reinforced by silicates or resin particles and a coupling agent (silane). The γ-methacryloxypropyltrimethoxysilane is subdivided into three parts in the figure below; M referring to the unsaturated

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methacrylate group capable of copolymerizing with the unfilled resin of a composite. The R refers to the spacer ((CH2)3) group. The X refers to the OSi(OH)3 or the group capable of chemically reacting with the surface. These three sub units combined together making up the M-R-X structure of the bonding agent.

Figure 18: γ-methacryloxypropyltrimethoxysilane, a typical silane which is used as a coupling agent with composite fillings. The commonly used dental composite is bis-GMA.

Figure 19: 2-methyl-2-Propenoic acid (1-methylethylidene) bis (4,1-phenylenoxy-2-Hydroxy-3,1-Propanediyl)) (Bis-GMA, Bowen’s Resin) Bis-GMA is an aromatic ester of dimethacrylate which is synthesized from ethylene glycol (epoxy resin) and methyl

methacrylate. The core of the two aromatic groups reduces its ability to rotate during polymerization. The two diagrams below show the steric stress caused by the two aromatic rings where the chain is forced to bring its two methacrylate groups at opposite ends of the chain together.

Figure 20: Stick model of bis-GMA.

Figure 21: Ball and stick model of bis-GMA. Like bis-GMA, all methacrylate monomers must be diluted because of their viscosity. Diluting methacrylate monomers brings the viscosity of the composite to a consistency that is workable for the dentist. Methacrylate monomers are diluted with either ethylene glycol dimethacrylate (EGDMA) or triethylene glycol dimethacrylate (TEGDMA). Composite resin materials contain numerous components in addition to the resin matrix, inorganic filler particles, and a coupling

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agent. 1, 2 Materials such as activation initiators, polymerization inhibitors and others that enhance the performance, appearance, and durability are also incorporated into the composite.2 The teeth are etched with phosphoric acid. The etching process prepares the teeth to allow the composite resin to bond. There are many types of bonding agents available as shown the diagrams below.

Figure 22: Amino-carboxylate based bonding agent (NPG-GMA)

Figure 23:Carboxylate-based bonding agent

Figure 24: Phosphate based bonding agent The activator-indicator system converts the soft resin paste into a moldable filling and then to a hard material and finally a filling which can withstand biting.2 The polymerization inhibitors prolong the shelf life of the composite.2 The coupling agent is vital that filler particles to bonded to the resin matrix, the coupling agent allows a flexible polymer matrix to address the concern of stress upon curing.2 Titanates and zirconates are other coupling agents which can be used. Organosilanes such as γ-methacryloxypropyl trimethoxysilane are more commonly used simply because the methoxy groups (-OCH3) under go hydrolysis to the silanol groups (-Si-OH) which bonds with the resin when polymerized which completes the coupling process.2

Composites are light activated or chemically activated. Blue light with a wave length of 470-nm is used in the light activation process. The blue light is absorbed by a photo-activator which is incorporated into the composite by the manufacturer.2 Organic amine containing a carbon double bond accelerates this mechanism. The camphorquinone (CQ) and amine are stable in the presence of the oligogmer at room temperature.

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Figure 25: Camphorquinone (CQ)2 The camphorquinone brings the composite paste to a slight yellow contrast making it difficult for the dentist to obtain the proper shade to match the other teeth. The chemical activation is done at room temperature. An organic amine reacts with an organic peroxide to produce free radicals that attack the carbon double bonds allowing for the polymerization process to begin.

Figure 26: The light-cure process gets activated when the camphorquinone absorbs a quantum of blue light and creates an excited-state complex with the dimethylaminoethyl methacrylate (DMAEMA) which is an electron donating amine. The figure above shows the unshared pair of electrons being donated by the amines to the ketone groups in the camphorquinone. Now that the camphorquinone is activated it extracts a hydrogen from the alpha-carbon and decomposes into the amine and CQ free radicals. The CQ free radical is readily inactivated and in the photoinitiation only the amine free radicals act to initiate the addition polymerization reaction (see figure 20).2

What’s free about free radicals?

Why start a reaction in your mouth?

There are three steps to free radical polymerization reactions which are initiation, propagation, and termination. Free radical molecules can be typically generated by a chemical, heat, visible light, ultraviolet light, or energy transfer from another compounds which acts as a free radical. In dentistry, chemical agents, heat, and visible light are used as the initiators to start the reaction. Chemical initiators are the most common used in the profession.

Initiation is the first step in the free radical polymerization reactions. The initiation step is started off by an external energy source which breaks a bond to produce the free radical(s). Free radical can be an atom or a group of atoms (a compound) with an unpaired shared electron that is used to initiate the sequences of reaction. R• can be any free radical.

To better explain the initiation stage, the disassociation of hydrochloric acid to hydrogen and calcium is shown in the reaction below.

H Cl H Cl

Heterolytic Bond Cleavage

Figure 27: Heterolytic Cleavage In the above reaction mechanism, the covalent bond in the hydrochloric acid is broken which results H+ and Cl-. Two bard curved arrow is used to point to the chlorine in the reaction to indicate that chlorine will have two unshared electrons. When electrons are distributed unevenly, in the initiation stage, such a reaction is referred to as a heterolytic bond cleavage.

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Cl Cl

Homolytic Bond Cleavage

Cl Cl

Figure 28: Homolytic Bond Cleavage The disassociation of molecular chlorine to produce 2Cl• is a homolitic bond cleavage. Notice that the single barbed arrows are used to show the distribution of the electron pair. In a homolytic bond cleavage, once the bond is broken, one electron is distributed to each of the chlorines. Your dentist uses one of three types of initiators to start a free radical polymerization reaction.

O

O

O

O

O

O

2

benzoyl peroxide benzoylradical

heat

Figure 29: Benzoyl peroxide Denzoyl radical Sufficient free radicals for polymerization may be produced at room temperatures by the reaction of a heat or chemical accelerator. Followed by this initiation stage is the quick addition of other monomer molecules to the free radical and the shifting of the free electron to the end of the growing chain. The initiation of a methyl methacrylate molecule (Figure 20).

Figure 30: Initiation of methyl methacrylate molecule. As the unpaired electron of the free radical approaches the methyl methacrylate molecule, one of the electrons in the double bond is attracted to the free radical to form an electron pair and a covalent bond between the free radical and the monomer molecule. In the process of forming these bonds, free radical molecules are created.2

The initiation of a dental resin, methyl methacrylate explained; as the unpaired electron of the free radical approaches the methyl methacrylate molecule (A & B), one of the electrons in the double bond is attracted to the free radical to form an electron pair and a covalent bond between the free radical and the monomer molecule (C & D). When this happens, the remaining unpaired electron makes the new molecule a free radical (D). The free radial-forming chemical used to start the polymerization is not a catalyst. This is because it enters into the chemical reaction and becomes apart of the final chemical compound. It is more accurately called an initiator because it is used to start the reaction. Many substances are able to produce free radicals and are potent initiator s for the polymerization of poly(methyl methacrylate) and other methacrylate-type resins used in dentistry.

Another type of induction system is chemically activated at the ambient oral temperature. This type of system consists of at least two reactants that, upon mixing together, they undergo a chemical reaction that generates free radicals. Because of their abilities to react these reactants must be stored separate from each other. Remember that chemically induced systems consist of two or more parts. A Tertiary amine (activator) and benzoyl peroxide (initiator), which are mixed together to initiate the polymerization of a self-cured dental resins at

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room temperature. Since the presence of amine reduces the thermal energy required to break the initiator into free radicals at ambient temperature, this reaction is considered to be heat activated.

Finally, the light-activated induction system is the third type. Photons from a light source activate the initiator to generate free radicals. These free radicals can initiate the polymerization process. When this system was first introduced to dentistry, ultraviolet (UV) light was used; however, due to other health complications visible light activated initiator systems were developed.

Figure 31: The Electromagnetic Spectrum19

Camporquione and an organic amine such as dimethlaminoethylmethacrylate generate free radicals when irradiated by light in the blue to violet region. A light source with a wavelength of about 470-nm is needed to trigger this reaction. Factors such as light intensity, angle if illumination, and distance of resin from the light source can affect the number of free radicals that are formed which is why this type of induction system is considered to be technique sensitive.

Figure 32: Propagation stage. When the initiated molecule reacts with the methyl methacrylate molecule, the electrons attack the double bond of the methyl methacrylate molecule. This process leads to what is known as the chain growth.2

Figure 33: Chain transfer. The process when the radical approaches the methyl methacrylate molecule and offers a hydrogen atom is referred to as chain transfer. The chain transfer causes the free radical to rearrange to create a carbon double bond to become unreactive.2

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Figure 34: Second type of chain transfer. When a propagating chain has interacted with a passive segment as formed in figure 23, another type of chain transfer has occurred. During this type of interaction the passive segment becomes active and the active segment becomes passive. 2

Figure 35: Termination. The final stage in the free radical polymerization is termination. Termination is reached when all of the free radicals have interacted and formed covalent bonds. 2

Free radical polymerization is how composites reach their high durability. The polymerized resin is highly cross-linked because of the dysfunctional carbon double bonds. The polymerization process of the light-cured composites varies according to the distance from the composite to the light and the time of exposure to the visible blue light. Monomethacrylate and dimetharylate monmers polymerize by the initiation of the free radicals.2 The free radicals which are required can be produced either by chemical

activation or by external energy activation such as heat or light. Considering the product produced at the termination stage, a hypothesis can be made that the carbonyl groups alter to create cross linkage, which leads to high resonance along the terminal ends of the highly conjugated structure. The aromatic rings at either terminal ends provide the composite resin tensile strength and make the resin bite worthy. Composite resins have become stronger and more resistant to wear. Polymer research has not developed a composite with the similar characteristics to that of amalgam. The use of composite fillers increases the chair time of a patient by approximately 10 to 20 minutes or longer. When large carries have formed, composite fillings may not last as long as amalgam fillings.

A major concern which has dentists resisting the use of composite fillings is their ability to shrink after curing. Often times, fillers can be added to reduce the shrinkage of the composite; however, shrinkage cannot be prevented.

You are probably familiar with cement and how it is used as a material in construction work. Just look around you when you are outside and bring your attention to the structures made of concrete.

How is cement made? What are its chemical properties? What is happening chemically to make it hard and strong? These are some questions you probably though about but never had answered. Cement is the binding agent in portland cement concrete (PCC). PCC is an inorganic material, or a mixture of inorganic materials, that sets and develops strength by chemical reaction with water by forming

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hydrates. This hydraulic powder type mixture solidifies when combined with water. There are several ways in which portland cement is manufactured. Regardless of which method is used, they all require similar chemical components and raw materials. Concrete is approximately 70% to 80% aggregate (filler material such as various grade rocks and/or sand) depending on which brand and type of concrete cement. The chemical components limestone (CaCO3), clay, shale (2SiO2 Al2O3), iron oxide (Fe2O3), silica sand (SiO2).20, 21 The afore mentioned materials are placed in a kiln and heated approximately 1400 to 1700oC. 3CaO ● SiO2, 2CaO ● SiO2, 3CaO ● Al2O3, 4CaO ● Al2O3 ● Fe2O3, are formed when the raw materials is heated to such extreme temperature which allows for them to react chemically. The product at the end of this heating process is the cement which is available for purchase at your local hardware store.

Figure 36: Cement Factory The described cement manufacturing process can be reviewed in depth at http://www.cement.org/basics/images/flashtour.html.22

Figure 37: Cement hydration21 Figure 27 provides a visual representation of cement hydration. The process begins with dissolution of grain particles followed by a solution of ionic concentration. Then compounds begin to form and upon reacting the point of saturation, solids begin to precipitate out as the products of the hydration process.21 A chemical reaction occurs when water and cement are mixed together, in chemistry we refer to this type of reaction as a hydration. Cement hydration is an exothermic reaction. The chemical compounds that harden the quickest are tricalcium aluminate and tetracalcium aluminoferrite. Gypsum is added to prevent the quick curing of the cement caused by tricalcium aluminate. Heat is generated by the hydration of tricalcium aluminate. The color of cement is due to tetracalcium aluminoferrite. Tetrachlcium aluminoferrite is used to vary the composition of cement. The hydration of tricalcium silicate provides the cement strength while it cures (hardens). The dicalcium silicate is responsible for the

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cement to strengthen over several days as it fully cures. So what actually is occurring chemically? Reaction 1: 2C3S + 7H C3S2H8 + 3CH ∆H = -500 J/g21 Reaction 2: 2C2S + 7H C3S2H8 + CH ∆H = -250 J/g21 The two reactions above are called hydration of calcium silicate reactions which produce calcium silicate hydrate and C-H. Reaction 2 produces half the amount of heat that reaction 2 produces. Reactions 1 and 2 are the source of the cement’s strength of the cement. Reaction 3: 2C3A + 3CSH2 + 26H C6AS3H32 ∆H = -1,350 J/g21 The hydration of the calcium aluminates is the source of this exothermic reaction. This reaction also produces needle-like interlocking structures which consume water, contributing to stiffening of mixture the and more resistant against sulfate attack.22 Figures 2 and 3 illustrate the hydration of calcium aluminates. When inspected closely hexagonal plates are formed in what geologist refer to as “rosettes” during the initiation of the hydration process. As the hydration process continues, the hexagonal plates grow and a susceptible to sulfate attack. The cement strength is based on multiple things, some of which are temperature, quality of cement and cement water ratio and cement to aggregate ratio. The strength assessments are conducted on cement sample which have settled for 1 day, 3 days, 7 days, 28 days, and 90 days. You might ask yourself why carry out a hardness test on a sample of cement after 90 days? Studies have revealed that cement can be curing into the 90th day. Understand that the

cement may look and feel as though it is fully cured however it is still polymerizing. We can say that after cement is allowed to settle for 90 days it is fully cured or has fully hardened.22

Most dental cements are supplied as a liquid and a powder component. Cements must exhibit a low viscosity to flow along the interfaces between hard tissue and a fixed prosthesis and they must be capable of wetting both surfaces to hold the prosthesis in place. The advances in resin chemistry for applications in dentistry have led to the development of resin based composite cements called rein cements. Dental cements are classified according to their chemical composition and bond strength to tooth structure when bonded with adhesives.

Dental composites are being used to restore teeth regardless of the location of their location and type of tooth in the mouth. Individuals choose to have composite resin filler rather then the amalgam filler mainly due to the physical appearance of the unnoticeable composition of the filler. The term composite in dentistry and material science has varied meanings. In material science a composite is a material comprised of two different phases and in dentistry the term is referred to as a particular group of materials.23 The group of materials all have two distinctive features about their structures. These materials are monomers which are based on bulky methacrylate monomers that set by free radical polymerization and are filled with a finely grained type of ceramic. The problems linked to the usage of 2-methyl-2-propenoic acid (1-methylethylidene) bis (4,1-pehnyleneoxy-2-Hydroxy-3,1-Propanediyl)) ester (bis-GMA), is that it has a high tendency to shrink when fully cured (hardened), it not as hard as traditional amalgam filling which is used in the molar teeth (rear teeth).

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Figure 38: Organic Monomers used in dental composite resin filling materials.23 The use of the large methacrylate chain has one disadvantage which is their high viscosities. In all applications for dental usage these methacrylate monomers must be diluted with either ethylene glycol dimethacrylate (EGDMA) or trethylene glycol dimethacrylate (TEGDMA). Using smaller monomers as diluents to obtain a viscosity which is much more comparable to work with; they have a larger polymerization shrinkage which increases the possible occurrences of micorleakages and fractures. It is best to reduce the dilution of Bis-GMA to greatly reduce the shrinkage factor; however, shrinkage cannot be totally avoided considering chemical composition of the composite resin.

Figure 39: Ball and stick model of ethylene glycol dimethacrylate (EGDMA)

Figure 40: Ball and stick model of triethylene glycol dimethacrylate (TEGDMA).

The shrinkage experienced by the methacrylates was seen to decrease as the molecular weight increased. Many research groups have confirmed that the polymerization shrinkage and molecular volume indicate that they are inversely proportional each other.24-26

Figure 41: Composition of dental cements.

When using methacrylate monomers

the polymerization process is never complete. The polymer contains many unreacted double bonds which range between 5 to 45% of the original concentration.23, 27, 28 The number of unreacted double bonds are based on several factors one of which is the composition of the monomer mixture.29, 30 One method often used to address polymerization contraction or other wise known as shrinkage or the uncured double bonds is a process often referred to as slow curing which is the process of allowing polymerization to occur slowly. Slow curing is a process where the composite

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resin is applied to the prepared carie in thin films and cured (hardened) to reduce the shrinkage caused by polymerization.

The crosslinking of a polymer structure is depended on the composition of the monomer from which the polymer was created. For example TEGDMA & Bis-GMA, result in an extremely high crosslink density. Asmussen’s study shows that the reacted double bonds increase with the amounts of bis-GMA in the bis-GMA & TEGDMA mixture.27 This study also indicates that the larger the percentage of remaining double bonds, the greater the chances of post shrinkage.27 The unreacted double bonds highlighted in the termination stage below allow for post polymerization to occur.

Figure 42: Unreacted double bonds

The information collected about the reacted double bonds, (RDB) was useful in order to understanding that the relative indication of low crosslink density and degree of softening of the composite sample being in ethanol. The more corsslinking that occurs, the harder the composite resin will be.

Figure 43: Monomer composition (mol%) remaining double bonds and Wallace hardness (HW, μm) before and after ethanol storage of the resulting polymers.

Figure 44: Content of CQ and CEMA (weight %) in a 60:40 (mol:mol) bis-GMA:TEGDMA monomer mixutre. Remaining double bonds (RDB%) and Wallace hardness (HW, μm) before and after ethanol storage of the resulting polymers. Post-Shrinkage Delphine Truffier-Boutry et al. have reported that the post-shrinkage is mainly due to the mobility of the chain and as mentioned earlier the continual polymerization process. The chemical explanation has been narrowed down to two sources which (1) are the free radicals and the double bond of the methacrylate groups or (2) free radicals causing the effect. Bergstrom et al. has arrived to the conclusion that polymerization could not possibly continue at 36oC.31 Truffier-Boutry states that many studies have been conducted to obtain an understanding if the initiation step, with different lamps which is a possible cause of the post polymerization.32

The use of dental cement as a restorative material began with silicate cement. Silicate cement is based on silicate glass and phosphoric acid. The glass for silicate cement was made by fusing compounds of silica (SiO2), alumina (Al2O3), fluoride compounds, and calcium salts at approximately 1400oC.2 Current approach for cementing prosthesis or applications is to use an adhesive. Adhesive bonding involves the

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placement of a third material called a luting agent (a viscous material placed between tooth structure and prosthesis that hardens through chemical reactions to firmly attach the prosthesis to the tooth structure)2 that flows within the rough surfaces and sets to a solid form. Cement paste must coat the entire inner surface of the crown and extend slightly. This is done to reassure that the space between the crown and the tooth is completely sealed.

Figure 45: A microscopic image of the prosthesis interfaces. (A) Shows the roughness of the two surfaces to be bonded and the imperfections. (B) Shows the two surfaces pressed against each other without the cement layer. (C) Shows the two surfaces and an intermediate layer which can be either cement or an adhesive. (D) Shows possible voids due to the inability of the intermediate layer to wet the surfaces.2 The State of the Art Composite Resin Considering the many types of fillers currently being used in dentistry, scientist, chemists and dentists are still in search for the ideal fillers to reduce shrinkage and stress to best be used as a filling in the mouth. This quest of scientifically creating a polymer based filling has taken Dr. Richard M. Laine to understand the behavior of the siloxanes.33

Nanomaterials can provide us with opportunities to expand our knowledge and allow us to find valid ways to use the material from a materials science perspective.

Dr. Laine reports in his review that the newly created cube shaped structures were derived from polyhedral oligomeric and octasilicate anions (OSA).33 The interesting aspect of the cubed structure of the octafunctional octasilsesquioxane is that they have a diameter in the rage of 1.2 – 1.4 nanometers.33

Figure 46: Typical size & volume of cube.34-36 Water is essential to the formation these cubes.33, 37 Their structure allows them to have a functional group in each octant either on opposite or completely orthogonal to each other. Very limited amount of knowledge has been gained in understanding the cube structures. The research conducted by Laine explains that nanocomposites have to be made in a specific way based on the purpose the composite is to serve in the oral cavity, this is to address the shrinkage factors which need to be considered in all composites. The ideal composite would be created with both hard and soft materials. The hard materials would act as the foundation of the composite and the soft material would shrink and stretch based on biting forces, polymerization, and temperature changes. The cube would be the hard material and the organic tethers would be the soft material.

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Figure 47: Example of organic tether.33

Figure 48: Example of an organic tether.33

Figure 49: Example of an organic tether.33

Figure 50: Example of an organic tether.33

Figure 51: Example of an organic tether.33

Figure 52: Example of an organic tether.33

The composites would be defined on the size and spatial relationships.33 If the organic tethers linking the cubes are short then they would allow for the possibility to create a microporous composite.

Figure 53: Continuous organic phase.

Figure 54: The blackened squares are the potential for controlled microporosity. Nanocomposite morphology which is disconnected. Nanocomposite with perfectly defined interfacial interactions.33 In the process of creating microporous materials, Laine33 reports the two methods were attempted to create a highly linked porous material. One which is a continuous matrix and another which was a microporous matrix. The chemistry behind these two matrices is not completely

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understood; however it is currently being further researched and studied.33

Figure 55: Schematic process of how the crosslinking occurs. Crosslinked polymer by hydrosilylation of oppositely functionalized cubes.33 Laine raises a very interesting point in his review33 about the epoxies which had been tested for shrinkage. Dodecyl methacrylate (DDM), was reacted with various epoxies and varying ratios of epoxy:amine at 150oC, the temperature that cures resin. Based on the results of these assessments it was determined that the curing chemistry of epoxy resin, two stoichiometries proved very minimal structural abnormalities which are when an epoxy reacts once with an NH2 or when two epoxy groups react with an NH2. This reaction is considered to be a defect because when the reaction proceeds, the resin viscosity increases where the complete reaction is inadvertently impossible. He also reports two scientific methods to place reactive methacrylate groups on the cubes with contaminant loss of methacrylate functionality or to retain their functionality.33 Hydrosilylation of the propargyl methacrylate can produce methacrylates, which gives tetraallylmethacrylate. This simple reaction will yield dicyclopentadiene platinum dichloride as a catalyst. It produces the

desired addition across the triple bond. At room temperature these materials are liquids, they cure by absorption of heat or a photochemical. Choi’s group has also further researched the cube structures. Similar to Laine’s groups Choi was not able to completely explain the chemistry; however they have realized that the amount of diaminodiphenylmethane (DDM) used to react with octakis(glycidyldimethylsiloxy)octasilsesquioxane (OG) effects how the cross linking takes place.

Figure 5638: The greater the amount of DDM used in the nanocomposite increase the changes of crosslinking to occur. Choi reports one tether can link four cubes together.38 Examining the figure below shows the ratio of epoxide groups to amine

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groups is 2 to 1 resulting in the organic tether to link up to four cubes.

Figure 57: Formation of nanocomposite.38 Not completely state of the art; however, further research by Hiroyuki Okamura and his team investigated on the formulation of a dental composite resin to further understand low-shrinkage and low-viscosity monomers. Their motivation of achieving such a monomer was supported by the fact that the task seemed to be achievable by using newly developed low-viscosity and low-shrinkage light curing monomers.39 Okamura and his group reported that each composite resin indicated an overall setting shrinkage of more than 80% in the first two minutes, the composites being exposed or irritated by the visible

light. The data collected by Okamura and group state that a significant difference was noted in the main effect of the monomer. The shrinkage was recorded to be the highest when the filler content was increased gradually starting at 50% of the composition of the composite resin.

Figure 58: Change of setting shrinkage of composite resin.39 The setting shrinkage decreased linearly with an increase in filler content. The composition of monomer mixtures used in this specific study is represented in the figure below.

Figure 56 shows the change in setting shrinkage of composite resins with the monomer composition. Based on this study done, it seems that the new monomer mixtures tended to cause small setting shrinkage. This small shrinkage may have been a result of the polyfunctional monomers and the small intermolecular distance. It is hypothesized that when polymerization occurred the decreasing

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Figure 59: The composition of monomer mixtures used in Okamura’s study.39 amount of intermolecular distance of the monomer would be comparable to the smaller molecule yet the decrease in the intermolecular space would be yet even smaller.39 Conclusion

Having conducted this investigation has revealed much in terms of the future of composite resin and the improvement which are to come. The composite Laine’s group has extensively studied and researched can be the ideal composite resin; however, there needs to be further studies conducted in terms of its biocompatibility in the oral environment. In regards to oral environment studies, there needs to a focus on the various food intakes and its interaction with the composite. The voids in one of the composites can be filled with an inorganic material which can alleviate the possibility of microleakage. The fact that the cubes have the ability to alter themselves after the initial reaction is a positive attribute of the

cubed structures which would address the shrinkage concerns of dentists. The crosslinking of the silsesquioxanes with the tethers is also another advantageous attribute. The crosslinking stabilizes the silsesquoxanes keeping the cubes from continuously rearranging themselves. There are many studies being conducted which all aim to reduce the polymerization shrinkage in some way. Various groups are performing further studies to advance the usage of the composite resin into the application of molar teeth is varying the ratio of bis-GMA to EDGMA or the ratio of bis-GMA to TEGDMA.30, 40, 41 Altering the ratio of the composite resin and diluents, has an affect on the cured volume of the polymerized composite resin. Studies have revealed that the greater amount of diluents used the greater the volumetric shrinkage is observed. Addition of inorganic particles has also resulted in the reduction of the polymerization shrinkage. Incorporating the

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inorganic particles reduces the shrinkage caused by acting as fillers to composite resin. Another aspect to be considered for further research is the bonding agent used to set all composites (MRX complex). The chemistry which supports this complex is not completely understood therefore further study and research can lead to a clear understanding of the chemistry related to the bonding agent.

There is a vast amount of research surrounding composite resins waiting to be explored and understood. Even though bis-GMA is a commonly used dental composite resin, the chemistry needs to be further understood in regards to reducing shrinkage and maintaining an acceptable hardness. As mentioned afore chemists and dentist are working to gain the needed insight to better the bis-GMA based composite resin and also explore the options to the ideal composite resin.

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Bibliography

1. John M. Powers, R. L. S., Craig's Restorative Dental Materials. Twelfth ed.; Mosby Elsevier: St. Louis, 2006. 2. Anusavice, K. J., Phillips' Science of Dental Material. 11th ed.; Saunders: St. Louis, 2003. 3. Powers, J. M., Tooth Anatomy. Medline Plus 200. 4. Powers, J. M., Tooth Anatomy. Medline Plus 2007. 5. Bratthall, D. Dental Carries - what is that? http://www.db.od.mah.se/car/data/cariesser.html (August 5, 2007), 6. Jacobs, J. http://www.nlm.nih.gov/medlineplus/ency/imagepages/1121.htm. http://www.nlm.nih.gov/medlineplus/ency/article/001055.htm (July 22), 7. IOCCC Dental Caries. http://www.lindt.ch/public/canada/chocomania/dental.pdf (July 22), 8. Ophardt, C. E. Virtual Chembook Sugar and Tooth Decay. http://www.elmhurst.edu/~chm/vchembook/548toothdecay.html (July 23), 9. Ellie, About Mouth Acids. 2007. 10. Bradbard, L. Dental Amalgam: Filling a Need or Foiling Health? http://www.fda.gov/bbs/topics/CONSUMER/CON0266g.html (July 26), 11. Berry, T. G.; Summitt, J. B.; Chung, A. K. H.; Osborne, J. W., AMALGAM AT THE NEW MILLENNIUM. J Am Dent Assoc 1998, 129, (11), 1547-1556. 12. Osborne, J. W. N., RD, 13-year clinical assessment of 10 amalgam alloys. Dent Master 1990, 6, (3), 189-94. 13. Letzel H van't Hof MA, M. G., Marchall SJ, The influence of the amalgam alloy on the survival of amalgam restorations: a secondary analysis of multiple controlled trials. J Dent Res 76, (1), 1787-98. 14. Berry, T., Osborne JW, Effect of zinc in two non-gamma-2 amalgam systems. Dent Master 1992, 1, (3), 98-100. 15. DNC, S. J. M. B. B. D. C., Shear bond strength of Amalgambond Plus cold and at room temperature. Journal of Dental Research 1998, 77, (Special issue A), 274. 16. O'Brien, W. J. Biomaterials Properties Database. http://www.lib.umich.edu/dentlib/Dental_tables/Creep.html (July 27, 2007), 17. Mahler, D. A., JD; Marek, M, Creep and Corrision of Amalgam. Journal of Dental Research 1982, 61, (1), 33-35. 18. Clarkson, T., Principles of Risk Assessment. Adv Dent Res 1992, 6, 22-27. 19. Chambers, L. H. The Electromagnetic Spectrum. http://mynasadata.larc.nasa.gov/ElectroMag.html (July 29), 20. Stephen T. Muench, J. P. M., Linda M. Pierce Portland Cement. http://training.ce.washington.edu/PGI/ (July 16), 21. Kurtis, D. K. Portland Cement Hydration; School of Civil Engineering: Atlanta, 2007; pp 1-18. 22. Association, P. C. http://www.cement.org/basics/index.asp (July 17, 2007), 23. Nicholson, J. W.; Anstice, H. M., The chemistry of modern dental filling materials. Journal of Chemical Education 1999, 76, (11), 1497-1501.

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24. Matsukawa S, H. T., Nemoto K, Development of high-toughness resin for dental applications. Dent Master 1994, 10, 343-6. 25. Chung CM, K. J., Choi JH, Synthesis and photopolymerization of dicarboxylic acid dimethacrylates and their application as dental monomers. J Appl Poly Sci 2000, 77, 1802-8. 26. M, G., Polymerization shrinkage of resin-based restorative materials. Aust Dent J 1983, 28, 156-61. 27. Erik Asmussen, A. P., Influence of selected components on crosslink density in polymer structures. European Journal of Oral Sciences 2001, 108, 282-285. 28. Ferracane JL, M. J., Condon JR, Todd R., Wear and marginal breakdown of composites with various degrees of cure. J Dent Res 1997, 76, 1508-1516. 29. E, A., Factors affecting the quality of remaining double bonds in restorative resin polymers. Scand J Dent Res 1982, 90, 490-496. 30. J L Feracane, E. H. G., The effect of resin formulation on the degree of conversion and mechanical properties of dental restorative resins. J Biomed Matter Res 1986, 20, 121-131. 31. Bergstrom J, V. G., Temperatures of the oral cavity in 50 healthy students Sewd Dent 1971, 64, 157-64. 32. D. Truffier-Bountry, S. D.-C., J. Devaux, J. Biebuyck, M Mestdagh, P. Paranois, G. Leloup, A physico-chemical explanation of post-polymerization shrinkage in dental resins. Academy of Dental Materials 2005, 22, 405-412. 33. Laine, R. M., Nanobuilding blocks based on the [OSiO1.5](x) (x=6, 8, 10) octasilsesquioxanes. Journal of Materials Chemistry 2005, 15, (35-36), 3725-3744. 34. N. Maxim, P. C. M. M. M., P. J. Kooyman, J. H. M. C. van Wolput, R. A. van Santen and H. C. l. Abbenhuis, Mg-Si-O and Al-Si-O Materials Derived from Metal Silsesquioxanes. Chem. Mater. 2001, 13, 2958. 35. R. H. Baney, M. I., A. Sakaibara and T. Suzuki, Silsesquioxanes. CHem. Rev. 1997, 95, (95), 1409-1430. 36. Matisions, A. P. a. J. G., Synthesis and applications of silsesquioxanes. Trends Polym. Sci. 1997, 5, (5), 327-333. 37. I. Hasegawa, S. S., K. Kuroda and C. Kato, The Effect of Tetramethylammonium Ions on the Distribution of Silicate Species in the Methanolic Solutions. J. Mol. Liq. 1978, (34), 307-315. 38. Choi, J.; Yee, A. F.; Laine, R. M., Organic/Inorganic Hybrid Composites from Cubic Silsesquioxanes. Epoxy resins of octa(dimethylsiloxyethylcyclohexylepoxide) silsesquioxane. Macromolecules 2003, 36, (15), 5666-5682. 39. Okamura, H., Miyasaka, T., Hagiwara, T., Development of Dental Composite Resin Utilizing Low-Shrinkage and Low-Viscous Monomers. Dental Materials Journal 2006, 25, (3), 437-444. 40. Moszner, N.; Salz, U., New developments of polymeric dental composites. Progress in Polymer Science 2001, 26, (4), 535-576. 41. Borkowski, K.; Kotousov, A.; Kahler, B., Effect of material properties of composite restoration on the strength of the restoration-dentine interface due to polymerization shrinkage, thermal and occlusal loading. Medical Engineering & Physics 2007, 29, (6), 671-676.

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Appendix A: Lesson Overview Teacher: Vishal Patel School: Mastery Charter High School Class: Chemistry/Science Topic: (Polymerization/Hydrogen Bonding) Academic Level: Honors Chemistry/AP Chemistry ______________________________________________________________________________ Title: Which type of Fillings would you prefer? ______________________________________________________________________________ Pennsylvania State Standard:1

3.2.10.A: Applying knowledge and understanding about the nature of scientific and technological knowledge.

• Compare and contrast scientific theories and beliefs. • Know that science uses both direct and indirect observation means to study the world and

the universe. • Integrate new information into existing theories and explain implied results.

3.2.10.C: Apply the elements of scientific inquiry to solve problems. • Generate questions about objects, organisms and/or events that can be answered through

scientific investigation. • Evaluate the appropriateness of questions

3.2.12.A: Evaluate the nature of scientific and technological knowledge. • Know and use the ongoing scientific processes to continually improve and better understand

how things work. 3.2.10.B: Apply process knowledge and organize scientific and technological phenomena in varied ways.

• Describe materials using precise quantitative and qualitative skills based observations. • Develop appropriate scientific experiments: raising questions, formulating hypothesis, testing

controlled experiments, recognizing variables, manipulating variables, interpreting data, and producing solutions.

• Use process skills to make inferences and predictions using controlled information and to communicate using space/time relationships, defining operationally.

3.4.10.A: Explain concepts about the structure and properties of matter. • Explain the formation of compounds and their resulting properties using bonding theories • Recognize formulas for compounds • Understand that carbon can form several types of compounds.

3.4.12.A: Apply concepts about the structure and properties of matter. • Apply rules of systematic nomenclature and formula writing to chemical structure. • Explain how the forces that bind solids, liquids and gases affect their properties.

3.2.10.D: Identify & apply the technological design process to solve problems.

1 http://www.pde.state.pa.us/k12/lib/k12/scitech.pdf Accessed August 13, 2007.

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• Examine the problem, rank all necessary information and all questions that must be answered.

• Propose and analyze a solution. • Communicate the process and evaluate and present the impacts of the solution.

3.2.12.D: Analyze and use the technological design process to solve problems.

• Assess all aspects of the problem prioritize the necessary information and formulate questions that must be answered.

• Propose, develop & appraise the best solution and develop alternative solutions • Implement and assess the solution redesigned and improve as necessary. • Communicate and assess the process and evaluate and present the impacts of the solution.

Objective: Students will be able to . . . . Explain variations in the chemical and physical properties of amalgam and composite fillings via an inquiry method. Identify the three stages in polymerization (initiation, propagation, and termination). Explain the process of Hydrogen Bonding. ______________________________________________________________________________ Materials: (Be sure to have enough for the class.) Day 1 Copies of Daily Learning Log worksheets2

Large post-it sheets/newsprint paper Markers Phillips Science of Dental Materials Restorative Resins Pages 399-441 Dental Amalgams Pages 495-543 Craig’s Dental Material Resin Composite Restorative Materials Pages 190-212 Amalgam Pages 236-267 On-line resource Published Journal articles

Amalgam vs. Composite Resin: 1998, by Gordon J. Christensen. Posterior Composite Resins: The Materials and their Clinical Performance, by Karl F. Leinfelder

Copies of three mini-labs Day 2 Daily Learning Log Thesis pages which describe polymerization steps One bag of Cheese Balls One bag of Cheese Puffs

2 Used with the permission of Megan Cubbage.

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One bag of Cheetos 30 Half toothpicks 55% Elmer’s glue solution in water 4% borax solution (sodium borate) Styrofoam cups Zip lock bags Food colors Several different polymer bottles Day 3 Daily Learning Log White sheet of paper Black sheet of paper Copies of Do Now Assignment ______________________________________________________________________________ Vocabulary: (There are the list of words which may need to be stress and explained to students.)

Polymers Macromolecules Initiators Monomers Crosslinkers Amalgam Composite Resin Cement Polymerization Initiation Propagation Termination Light Curing

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Which type of Fillings would you prefer? DAY 1

______________________________________________________________________________ Prep Teacher will write the following Do Now assignment on the board. We will be discussing amalgam and composite resin fillings. Fill in the Prior Knowledge section of the Daily Learning Log. ______________________________________________________________________________ Objective Students will be able to. . Explain the two types of filler and the chemistry which is associated with each of them. Students will review journal articles, World Wide Web and text books to gather the information they need to use in their debate. ______________________________________________________________________________ Pennsylvania State Standard:3

3.2.10.A: Applying knowledge and understanding about the nature of scientific and technological knowledge.

• Compare and contrast scientific theories and beliefs. • Know that science uses both direct and indirect observation means to study the world and

the universe. • Integrate new information into existing theories and explain implied results.

3.2.10.C: Apply the elements of scientific inquiry to solve problems. • Generate questions about objects, organisms and/or events that can be answered through

scientific investigation. • Evaluate the appropriateness of questions

3.2.12.A: Evaluate the nature of scientific and technological knowledge. • Know and use the ongoing scientific processes to continually improve and better understand

how things work. ______________________________________________________________________________ Do Now: (5 MIN. Independent activity students complete upon entering classroom.) Teacher will greet each student at the door, hand out the Daily Learning Log and monitor classroom. Students are to work independently on the Do Now assignment. Students are not permitted the use of any resources for the duration of this activity. ______________________________________________________________________________ Direction Instruction: (I do; What teacher will do to guide the students in the learning process.) DAY 1 Activity (Time) During class teacher will . . . During class students will. . . • Begin lesson by

dividing the students in to small groups (four

3 http://www.pde.state.pa.us/k12/lib/k12/scitech.pdf Accessed August 13, 2007.

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students per group). There should be a reporter, script, group monitor, and leader in each group.

First Activity (10 MIN.) Lecture

• Provide students with baseline information on amalgam and composite fillers.

• Have students who have had fillers applied in their mouths share their experience. (To obtain students’ attitude about science in the real word)

• Teacher is limiting formal lecture to 10-min. to allow for inquiry learning to occur and to host a student centered classroom by allowing students to independently investigate

• Pay attention to lecture and take notes.

Second Activity (25 MIN) • Explain the following to the groups.

• Each group will have a different set of resources on amalgam or composite resin fillers. One group has web, test, & journals. Your task for the next 25 minutes is to review the information and be ready to report to the class your findings/new learning.

• Each group will be given a set of resources about amalgam or composite resin fillers. You are to review the resources in your groups.

• Each group is required to take notes from what you read; however, the resources are not to leave the room.

(15 MIN) • Let students know that they may want to take notes on what they learn from the group reports.

• Go around the room and select volunteer group reporters to report to the whole

• Remain silent while the elected group reporter completes his/her duties to share the groups’ information with the whole class.

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class the groups’ information.

• Emphasize polymerization and shrinkage. Explain the process of polymerization.

• Explain hydrogen bonding and the role it plays in the composite resin.

• Review teacher’s notes and stress the points of importance to the class.

______________________________________________________________________________ Exit Assessment: (You do: How will you assess if the students acquired the skill for today) Students will complete the last three sections of the Daily Learning Log and submit to teacher. ______________________________________________________________________________ Homework: (You do: An extension to the content covered in class.) Teacher will distribute the lab for the following day for students to prepare pre-lab reports. ______________________________________________________________________________ Teacher Notes: Limit direct instruction to ten minutes. Having the lecture limited to ten minutes will provide an ample amount of time for teacher to provide the baseline information students will need to begin thinking about the types of filler; however, it will make them interested in the types of fillers to investigate them in small groups. In small groups the type of resource will be different for each group. The table below indicates the resource and what will be the groups focus.

Groups Number Type of Resource Type filler to focus on 1 Dental Text Amalgam 2 Dental Text Composite Resin Filler 3 Journal Article Amalgam 4 Journal Article Composite Resin Filler 5 World Wide Web Amalgam 6 World Wide Web Composite Resin Filler

Students will be given twenty-five minutes to investigate in small groups and gather information about either the composite resin or amalgam they feel is important for them to share with the whole class.

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After the twenty-five minutes of small groups investigation, a selected reporter will report their findings to the whole class, where they will be required to answer questions their classmates have about the information they report to the class. During the sharing of information, students will be taking notes to develop a deeper understanding of the information which is shared with their class makes. The Daily learning log will be handed in by all students. Daily Learning Log is used to assess the students’ understanding of composite resin and amalgam fillers and the chemistry associated with each of them. The Daily Learning Log also allows students to relate daily topics to their lives, ask clarifying questions, and restate what was taught in class and how comfortable they are with the material. During the last five minutes students will be lead in an organized whole class discussion to close the class with the highlighting the make points of the class.

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EXPERIMENT 14

Crunch and Munch Lab

Desk Top Building of Polymer Chain Components

Objective: The objective of this lab is to introduce the concepts and vocabulary of "polymers" with simple models.

Review of Scientific Principles:

Polymers (Greek-POLY...many and MEROS...parts) have existed since the beginning of life. Both "natural" and "synthetic" polymers are an integral part of our life. Most of the natural and synthetic materials with which we come in contact are wholly or partly polymeric in nature.

Polymers (plastics) are large molecules (macromolecules) made up of repeating units called "mers" or more correctly "monomers". These "units" are chemical molecules. To introduce the common terms used in polymers, we will use the models shown in this desktop experiment.

Time: This laboratory experiment requires about 40 minutes.

Materials and Supplies:

30 half toothpicks

Procedure:

1. Remove the initiators from the bag that you were given. Record your bag number. Add a toothpick and than a monomer to each initiator. Continue to add toothpicks and monomers to chain until all the monomers have been used. (Don't eat the experiment.)

Different polymers have different types, shapes, and numbers of monomers. The initiators are used only in addition polymerization reactions like those we are modeling in this experiment (there are also condensation types of polymerization). The initiators which start the polymerization reaction are a group of chemicals called "free radicals". These chemically

4 http://matse1.mse.uiuc.edu/polymers/d.html Accessed August 1, 2007.

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unstable groups are formed by tearing apart a normally stable molecule so that there is an unpaired electron (pairing produces stability) in some part of the chemical segment.

2. Using toothpicks, connect the partial chains together at the ends which do not have "initiators" located on them. Continue the connection until all the partial chains have been used.

3. Using the ends of the crosslinker with the attached toothpick, connect the chains together (cross-link). The connection of chains together along their body is called cross-linking. The synthetic process has an origin as far back as "vulcanization" in which sulfur was used to cross-link natural rubber in making and patching tires. In later experiments, we will be using borax as a cross-linking agent.

Questions:

1. Describe (define) a polymer in your own words. 2. Draw your polymer and the polymers of two other people who have different numbers on

their bags. It should be noted here that normal polymers have literally tens to hundreds of thousands of monomers making up a chain instead of the sparingly few that you have been given to use.

3. As the number (concentration) of initiators increase, what happens to the length of the chains? (Note: You will have to compare the above structure to those of other students.)

4. How (predict) do the "strength" and "flexibility" of the polymers change as the number (concentration) of cross-linkers increases.

a) A "branched polymer" is formed when one chain is attached along the body of another chain. A branched polymer resembles the branches of a tree. Redraw your structure so that it shows branching.

b) What did you have to do with one of the terminal ends in order to create the branching requested for your polymer?

5. Below is the structure of benzoyl peroxide (used in acne medicines). Separate the molecule to show two identical free radicals.

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6. Below is the polymer of PVC, Poly(Vinyl) Chloride. Circle the repeat unit of this if is was made from ethylene.

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Teachers Copy

Teacher Notes:

Objective: The objective of this laboratory is to learn the vocabulary of polymer synthesis through the making of models. This is a very simplistic modeling lab. The terms used will have meaning and purpose as a result of this desk top lab.

Review of Scientific Principles:

We will be using cheese snack foods to present models in addition polymerization and cross-linking of the polymer chains. All of these materials may be obtained from a grocery or discount store. Starch or Styrofoam peanuts may be used instead of food products if the maturity of the class is in question.

Students at this point have no background for condensation polymerization and it is suggested that nothing but its existence be noted at this time. A more "in-depth" presentation will be made later in the module.

Free radicals are introduced as initiators to the polymerization process. The formation of a sample radical and its action on a monomer may be described as:

In the presence of UV light or other high energy sources, a monomer may also form a radical. In this section the cross-linker and monomer were considered as totally different. This self initiating and/or self cross-linking of the monomer should not be presented to the student at this time. The ethylene above can alter the double bond forming the unstable radical (shown bellow) as it is struck by UV light.

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A popular example of a harmful radical is one formed by the types of Chloro-Fluoro-Carbons that we use as refrigerant gases.

Of course, the very reactive ozone of the ozone layer of the atmosphere may cause the same reaction, also forming the unstable radicals.

Time: The preparation time for this lab is about 30 minutes.

Procedure:

Three classes of bags should be filled and numbered as follows:

Bag # Cheese balls Cheese Puffs Cheeto Crunchies

1 4 20 2

2 7 20 4

3 10 20 7

Answers to Questions:

1. A high molecular weight macromolecule made up of multiple repeating units. 2. Students should have only one attachment on each initiator. 3. The greater the number of initiators or concentration of initiators, the shorter will be the

length of the straight chain of the polymer. 4. As the concentration of cross-linkers increase, the flexibility/fluidity of the polymers will

decrease. This explanation can be likened to the fact that as the number of steps on a ladder increase, so will the stability of the ladder. Those students having an odd # of initiators will already have a branched polymer in this model. In the normal polymerization "branching" will occur as part of the normal process regardless of the number of initiators. Students that had an even number of initiators could do one of two things: a) they could remove one of the initiators from one of chains to make the connection. b) they could break one of the chains making a branch with each segment.

5.

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6.

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EXPERIMENT 25

Slime Away

Cross-Linking Poly (vinyl alcohol) with Sodium Borate

Objective: The objective of this experiment is to explore the change in physical properties of a polymer as a result of cross-linking. The result of adding more cross-linking agents to a polymer is considered and another model of cross-linking is viewed.

Applications:

There are a number of uses of the PVA polymer we are studying:

1. They may be used in sheets to make bags to act as containers for pre-measured soap you simply throw into a washing machine.

2. The PVA sheets may be made into larger bags to be used by hospitals as containers for the cotton cloth used in the operating rooms or to hold the bed linen or clothing of infected patients.

Time: This experiment will require approximately 15-20 minutes to run and clean up.

Materials and Supplies:

• 100 ml/group of poly (vinyl alcohol) 4% • 10 ml of sodium borate 4% • Styrofoam cups and wooden stir sticks (tongue depressors) • Zip lock bags or latex gloves (surgical)

General Safety Guidelines:

• Laboratory aprons and goggles should be worn in this experiment as in all procedures.

• Both the borax and the PVA will burn the eyes. Hands should be washed at the end of the experiment.

5 http://matse1.mse.uiuc.edu/polymers/e.html Accessed August 1, 2007.

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Procedure:

The polyvinyl alcohol and sodium borate are mixed together in approximately a 10 to 1 ratio.

1. 100 ml of the 4% poly (vinyl alcohol) is added to a Styrofoam cup . 2. Food coloring can be added to the PVA in the cups to make different colors. Simple food

coloring is recommended. This coloring should be added before any of the borax solution has been added, or it can be added directly to the borax solution.

3. Add 10 ml of the 4% cross-linker (sodium borate) to each cup. Begin stirring the mixture immediately with your wooden tongue depressor.

4. Make observations as to what is occurring as the reaction proceeds. 5. Within a couple of minutes the slime will be formed. Lift some of it out with the tongue

depressor and make your observations. Record your observations on your data sheet. 6. Take some in your hand and stretch the slime slowly. Record your observations on your data

sheet. 7. Repeat the stretching exercise only this time do it rapidly. Record your observations on your

data sheet. Compare the results of the two tests. The slime is non toxic and is safe to handle, so you can put it in a Zip-lock bag (or latex glove) and seal it to take home.

8. Follow good laboratory procedure and wash your hands with soap and water. It is recommended that this procedure be followed whenever handling this material. Keep it in the glove or bag until it is discarded. The sodium borate or PVA could burn your eyes.

9. Place a small amount of the PVA on a paper towel and set it off to the side to dry until tomorrow. Upon returning to class the next day, record in the data section your observation of the slime.

Data and Analysis:

Observation of the PVA before the sodium borate is added:

Observation of the PVA after the sodium borate is added:

Observation of stretching the cross-linked PVA slowly:

Observation of stretching the cross-linked PVA rapidly:

Observation of the cross-linked PVA left out in the air overnight:

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Questions:

1. What are the physical properties that change as a result of the addition of sodium borate to the poly (vinyl alcohol).

2. What would be the effect of adding more sodium borate to your cup (your thoughts only)? 3. After making the observations on the dried PVA, how does the water affect the elasticity of

the polymer? What is elasticity? 4. Find and circle the repeat unit in the polymer molecule below?

5. What is the formula of the poly (vinyl alcohol) monomer circled above? (Your teacher may

want to show you how to alter this slightly after you have drawn the structure.) 6. In the picture below, circle the borax cross-linking agent.

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TEACHER COPY Teacher Notes:

Objective: The objective of this experiment is to explore the change in physical properties as a result of cross-linking polymers. The results of the addition of more cross-linking agents are considered and another model of cross-linking is viewed. Students also have an opportunity for monomer identification.

Experimental:

1. The Polyvinyl Alcohol as a solid is mixed in water to make a 4% solution. That is 40.0 grams of PVA per 960 grams (milliliters) of water. The best results are obtained by heating the water to about 80oC on a hot plate with magnetic stirrer. Sprinkle the PVA powder in very gently and slowly on the top of the solution while stirring so as not to cause the mixture to clump together. Temperatures above 90oC may result in decomposition of the PVA and perhaps the creation of an odor to the solution. Continue to sprinkle the PVA into the hot solution while it is stirring. After all of the PVA has been added to the water, place a top on the vessel. If the water evaporates off, a skin of PVA will form. This PVA sheet might also be a nice item to lift off and show the students. Continue stirring until the mixture is uniform (note also that it will be somewhat viscous). Allow the solution to cool, and the resulting solution will be ready for the students to use.

2. If students are adding a dye to their PVA, make sure they do this before the addition of borax.

3. The borax (sodium borate) can be obtained from your grocery store as "Twenty Mule Team Borax," a laundry bleaching agent. The borax is mixed at a 4% concentration in water. To do this measure out 4 grams of borax and dissolve in 96 grams (milliliters) of water (note: Water has a density of 1 g/mL).

4. The material becomes more viscous as we mix the PVA and the borax. It will reach a maximum level of viscosity and will not thicken further without more cross-linking agent. The addition of a higher ratio of Borax will result in a very viscous polymer (like Jell-O).

Theoretical:

The polymer used is "poly (vinyl alcohol)". The monomer has a formula of:

• Borax is sodium borate, Na3BO3. The borax actually dissolves to form boric acid, H3BO3. This boric acid-borate solution is a buffer with a pH of about 9 (basic). Boric acid will accept a hydroxide OH- from water as indicated on the next page.

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The hydrolyzed molecule will then act in a condensation reaction with PVA as indicated in the last question on the student laboratory.

• In the above illustration, two PVA molecules are shown being cross-linked by a hydrated borax molecule. Four molecules of water are also produced.

• The resulting material is about 95% water. It is the water that gives the polymer flexibility. Note that as the polymer dries it returns to its solid phase now as a sheet that is rigid and almost transparent.

• The PVA does not dissolve easily in water. Prepare the PVA solution at least one day in advance.

• Guar Gum dissolves in water much more easily than PVA, but seems to "jell" at a much more unpredictable rate than the PVA mixture does. For this reason, PVA is preferred.

Additional reading for more in depth information can be found in:

Journal of Chemical Education, Jan. 1986, #63, pp. 57-60.

Sample Data and Analysis:

Observation of the PVA before the sodium borate is added: The solution is fluid.

Observation of the PVA after the sodium borate is added: The mixture becomes more viscous (thicker).

Observation of stretching the cross-linked PVA slowly: The slime flows and stretches.

Observation of stretching the cross-linked PVA rapidly: The slime breaks.

Observation of the cross-linked PVA left out in the air overnight: It became a dry film.

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Answers to Questions:

1. The mixture becomes more viscous (thicker). 2. The mixture would jell. 3. The ability of the cross-linked polymer to stretch decreases. The polymer becomes more

brittle and will break.

4. 5. C2H3OH 6. The hydrated borax, minus the four hydrogens are shown on the previous page bonding two

chains of the PVA polymer together.

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EXPERIMENT 36

A Silly Polymer

Cross-Linking a Polymer to Create Everyone's Favorite Childhood Toy, Silly Putty

Objective: The objective of this experiment is to cross-link a polymer and observe the changes in the physical properties as a result of this cross-linking. The changes in physical properties of a cross-linked polymer are also studied as the temperature is varied.

Review of Scientific Principles:

If a substance springs back to its original shape after being twisted, pulled, or compressed, it is most likely a type of polymer called an elastomer. The elastomer has elastic properties (i.e., it will recover its original size and shape after being deformed). An example of an elastomer is a rubber band or a car tire.

The liquid latex (Elmer's glue) which you use contains small globules of hydrocarbons suspended in water. The silly putty is formed by joining the globules using sodium borate (a cross-linker). The silly putty is held together by very weak intermolecular bonds that provide flexibility around the bond and rotation about the chain of the cross-linked polymer. If the cross-linked bonds in a polymer are permanent, it is a thermosetting plastic, even if above the glass-transition temperature (Tg). If the bonds are non-permanent, it can be considered either thermoplastic or an elastomer.

Time: A 20-25 minute period is required to perform the mixing/making of the silly putty.

Materials and Supplies:

• 55 % Elmer's glue solution in water • 4 % borax solution (sodium borate) • Styrofoam cups • zip lock bags • food colors

General Safety Guidelines:

• Since borax solid (a bleaching agent) and solution will burn the eyes, goggles and aprons should be worn.

• Hands should always be washed after kneading the silly putty and finishing the experiment.

6 http://matse1.mse.uiuc.edu/polymers/f.html Accessed August 1, 2007.

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Procedure:

1. Wear goggles and lab aprons. 2. Pour 20 ml of the Elmer's glue solution into a Styrofoam cup. 3. Add 10 ml of the cross-linker (borax solution) to each cup. 4. Immediately begin stirring the solutions together using the wooden stick. 5. After a couple of minutes of mixing, the silly putty should be taken out of the cup and

kneaded in the hands. Don't worry about the material sticking to your gloves as these pieces will soon mix with the larger quantity with which you are working. Continue to knead until the desired consistency is reached.

6. Using a ruler to measure, drop the ball from a height of 30 centimeters. To what height does it rebound?

7. Stretch the silly putty slowly from each side. 8. Compress the silly putty back into a ball. 9. Pull the silly putty quickly from each side and compare the results. 10. Place the silly putty on some regular news print and press down firmly. 11. Remove the silly putty from the news print and make observations. 12. Repeat the same procedure on a comic section of the newspaper. The silly putty is non-toxic

and safe to handle so you can put it in a zip-lock bag and take it home. 13. Follow good laboratory procedure and wash your hands with soap and water when you have

finished the experiment.

Data and Analysis:

Height of the rebound _________ cm.

Observations of pulling the silly putty slowly:

Observations of pulling the silly putty quickly:

Observations of the silly putty on newsprint:

Observations of the silly putty on the comic's section of the newspaper:

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Questions:

1. How do the physical properties of the glue, water mixture change as a result of adding the sodium borate?

2. What would be the effect (your thoughts) of adding more sodium borate solution? 3. What is the ratio of the height of the drop to that of the rebound distance? 4. Who in the class had the ball with the most elasticity? 5. How did you come to the conclusion of whose ball was most elastic?

At Home: -Place your ball in the refrigerator for 10 minutes. Recheck the bouncing portion of this experiment.

6. What are your observations? 7. Why do you think this was observed?

-Now place your ball about 6 inches from a light bulb for about 5 minutes and again recheck the bouncing portion of this experiment.

8. What are your observations? 9. Why do you think this happened?

Explain the Following:

1. Why does a car tire appear to be flat in the summer even though the gas inside is hotter than in the winter.

2. Why does a basketball bounce differently inside a gym than it does outside on a cold wintry day.

3. Why will a tire sometimes bump during the winter as a car is moving, only to smooth out its ride after the car has been traveling for a distance.

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Teachers Copy

Teacher Notes:

Objective: The objective of this experiment is to investigate cross-linking using a similar technique as was used in the making of slime. The same parameters are worked again with a formal and a quantitative measurement used to describe elasticity. The added home investigation of the effect of temperature on the elasticity also includes concepts of molecular motion and intermolecular bond strength.

Review of Scientific Principles:

If a substance springs back to its original shape after being twisted, pulled, or compressed it is a type of polymer called an elastomer. The elastomer has elastic properties. It will recover its original size and shape after being deformed.

The liquid latex used contains small globules of hydrocarbons suspended in water. Joining these globules forms the mass with which the students will be working. The covalent bonds along the chain are strong, but the bonds between chains are normally weak. However, additives such as borax allow the formation of strong "cross-links" between chains, such as C-B-C. As the number of cross-links increases, the material becomes more rigid and strong.

If the rigidity of a polymer is noticed to decrease when a critical temperature is reached, the polymer is called a thermoplastic. If the bonds between polymer molecules are very strong, the material decomposes before any softening occurs. Such a material is called a thermoset plastic.

Natural sources of this liquid latex are milkweed, rubber trees, pine trees, aloe plants, and many desert plants. This latex is used to quickly mend and repair any damage to the outer covering of the plant.

General Safety Guidelines:

• The materials used in this experiment are all non toxic. It is a good idea always to exhibit good laboratory technique when working with the students. Make sure the laboratory.

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Experimental:

There are many variations of this experiment.

1. The original silly putty was prepared using sodium silicate and mixing this with borax. 2. A variation also exists using laundry starch and mixing it with borax. 3. Similar variations also exist by sprinkling the borax evenly and gently over the solution of

latex then working it with the hands. This does not require as much kneading to dehydrate the sample.

Time: - About 15 minutes are required to ready solutions, cups and tongue depressors. 10-15 minutes will be required in lab for testing and clean up. The students will require 10-15 minutes of work at home in order to finish all of the experimental work on this laboratory and the write up.

Answers to Questions:

1. The liquid type of starting material should jell and become more viscous as cross-linking occurs.

2. The material will become more solid or rigid. 3. Student answer. This is only a method of measuring elasticity of the polymer. Stretching

gives a similar means of comparison. 4. Student answer. 5. Greatest rebound to drop height ratio. 6. Here the student will be studying the effect of temperature variation on elasticity. Students

are sometimes surprised if they place their sample into a freezer rather than a refrigerator. The results are that the ball will shatter rather than bounce.

7. The ball should be more elastic. 8. Contrary to what some students will predict, should the ball become too warm, the resulting

ball will deform rather than continue to increase in elasticity. 9. The ball deformed rather than rebounding.

-All of the answers to the questions in the EXPLAIN THE FOLLOWING section involve the use of principles previously presented in this laboratory.

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Which type of Fillings would you prefer? DAY 2

______________________________________________________________________________ Prep: Teacher will have on board. Be seated in your lab groups at your lab stations. REMINDER: A copy of your pre-lab must be handed in before you leave lab. Teacher should prep for lab. Obejctive: Students will be able to. . . Understand the vocabulary of polymer synthesis by creating models. Explain the processes of polymerization (initiation, propagation, & termination). Understand the change in physical properties of a polymer by crosslinking. Identify monomers ______________________________________________________________________________ Pennsylvania State Standards:7

3.2.10.B: Apply process knowledge and organize scientific and technological phenomena in varied ways.

• Describe materials using precise quantitative and qualitative skills based observations. • Develop appropriate scientific experiments: raising questions, formulating hypothesis, testing

controlled experiments, recognizing variables, manipulating variables, interpreting data, and producing solutions.

• Use process skills to make inferences and predictions using controlled information and to communicate using space/time relationships, defining operationally.

3.4.10.A: Explain concepts about the structure and properties of matter. • Explain the formation of compounds and their resulting properties using bonding theories • Recognize formulas for compounds • Understand that carbon can form several types of compounds.

3.4.12.A: Apply concepts about the structure and properties of matter. • Apply rules of systematic nomenclature and formula writing to chemical structure. • Explain how the forces that bind solids, liquids and gases affect their properties.

______________________________________________________________________________ Do Now: (5 MIN. Independent activity students complete upon entering classroom.) Teacher will greet each student at the door, hand out the Daily Learning Log and monitor classroom. Students are to work independently on the Daily Learning Log. Students are permitted to use the resources available to them (not the help of other students). Hand out copies of thesis paper which describes the polymerization steps.

7 http://www.pde.state.pa.us/k12/lib/k12/scitech.pdf Accessed August 13, 2007.

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While students are working on Do Now assignment, teacher should attend to administrative duties and reinforce lab safety. Teacher should check to maximize groups of four students to minimize chemical wastes. ______________________________________________________________________________ Direction Instruction: (I do; What teacher will do to guide the students in the learning process.) Activity (Time) During class teacher will . . . During class students will. . .5 MIN • Begin lesson by

addressing lab safety. • Stress to student that

eating and drinking in the lab is strictly prohibited.

• Explain to students that they will be doing three mini labs during this lab day. They have the full lab period to work with last ten minutes to clean up. They can work in any order they choose.

• Students will gather into their groups.

20 MIN Slime Away 40 MIN Crunch and Munch 25 MIN A Silly Polymer

• Circulate around the room to reinforce lab safety.

• Complete 3 mini-labs and submit pre-lab before leaving.

Some time throughout the lab

• Write on board and bring to the attention of students some time throughout the lab.

• Lab reports are due in one week. Each mini lab must be written up separately with all post lab questions answered.

• Should read and write down at some point during the lab.

Last 15 minutes • Teacher should inform students to begin cleaning up and wipe everything down.

• Teacher will close period by reinforcing the purpose of completing the three mini-labs.

• Students should finish what they are working on, clean up and have lab experiment data out to be initialed before they exit the lab.

______________________________________________________________________________ Exit Assessment: (You do: How will you assess if the students acquired the skill for today)

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Students will have they lab data initialed before they leave the lab & complete Daily Learning Log. ______________________________________________________________________________ Homework: (You do: An extension to the content covered in class.) Students will work on completing the lab write up due next lab period. ______________________________________________________________________________ Teacher Notes: The Do Now assignment is administered as an informal assessment to inform the teacher of who need reinforcement/remediation. This specific Do Now will be reviewed before the beginning of the lab. The reinforcement/remediation should take place sometime through the class periods by pulling several students from each small group. (At this time if the students who have been identified for reinforcement, have questions they should be allowed to ask them before selecting students who understand the concept (this is due to the limited time).

During this class period students will be working on mini-labs at stations set up throughout the classroom. Students will be in their assigned lab groups. It is the responsibility of each group to complete the three mini labs set up. During the time students are working on the mini-labs, teacher will be monitoring that students are practicing proper lab safety.

During the last fifteen minutes of class, teacher will lead the class in a discussion to reinforcement the purpose of the three mini labs which were.

• Understand the vocabulary of polymer synthesis by creating models. • Explain the processes of polymerization (initiation, propagation, & termination). • Understand the change in physical properties of a polymer by crosslinking. • Identify monomers

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NAME: DATE: DO NOW-DAY 2 Answer the following questions to the best of your ability. You are to work independently and you are not allowed to use any resources. Identify the following polymerization stages.

1.

BrC C C CBr

C CBrH Br C CBr BrH +

2.

BrBr BrBr

C CBr Br C CBr Br

3. Br Br Br2

4.

R O O R heator hv R O O R+

R O H Br heator hv R O Br+H

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Which type of Fillings would you prefer? DAY 3

______________________________________________________________________________ Prep: Teacher should have the room set up so the desks are in two large groups. Teacher is to select a method of randomizing students into the two groups. In the center of one group of desks place a white piece of paper representing composite and at the center of the other group of desk place a piece of black construction paper representing amalgam. ______________________________________________________________________________ Objective: ______________________________________________________________________________ Student will. . . Defend either amalgam or composite fillers using supporting chemistry knowledge as evidence. Pennsylvania State Standard:8

3.2.10.D: Identify & apply the technological design process to solve problems.

• Examine the problem, rank all necessary information and all questions that must be answered.

• Propose and analyze a solution. • Communicate the process and evaluate and present the impacts of the solution.

3.2.12.D: Analyze and use the technological design process to solve problems.

• Assess all aspects of the problem prioritize the necessary information and formulate questions that must be answered.

• Propose, develop & appraise the best solution and develop alternative solutions • Implement and assess the solution redesigned and improve as necessary. • Communicate and assess the process and evaluate and present the impacts of the solution.

Do Now: (5 MIN. Independent activity students complete upon entering classroom.) Teacher will stand by door to greet students and hand out Daily Learning Log. ______________________________________________________________________________ Direction Instruction: (I do; What teacher will do to guide the students in the learning process.) Activity (Time) During class teacher will . . . During class students will. . .5 MIN • Explain to the students

that they will be having a debate about the two types of fillers used in dentistry. Teacher should explain the rules

• Pay attention and understand their responsibility for the first activity.

8 http://www.pde.state.pa.us/k12/lib/k12/scitech.pdf Accessed August 13, 2007.

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of debating. (Each group member is required to state one fact about the filler before the debate begins each group will be allowed to comment when they are called on.) Explain to students that they will have 30 minutes to review the literature to find chemistry facts on the specific filler they are to defend.

20 MIN Review Literature (First Activity)

• Monitor and sit in on group that need help/assistance.

• Make sure that both groups understand what it is to have chemistry evidence to support their facts.

• Scan literature to find information on their specific filler and any chemistry information to support their filler.

15 MIN Debate (Second Activity)

• Over see • Each student will state a fact about the filler they are defending

10 MIN (Summary) • Teacher should highlight the points made by both groups however should not favor either type of filler. Allow the students to even consider further study/understand the types of filler.

• Pay attention, pose questions to confusing points made in class by teacher.

______________________________________________________________________________ Exit Assessment: (You do: How will you assess if the students acquired the skill for today) Students will complete a Daily Learning Log ______________________________________________________________________________ Homework: (You do: An extension to the content covered in class.) Students will work on write a one page paper support either amalgam or composite resin fillers using chemistry facts as supporting evidence.

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NAME: DATE: DO NOW-DAY 3 Answer the following questions to the best of your ability. You are to work independently and you are not allowed to use any resources. Make a list of all the facts you remember about amalgam and composite resin fillers. AMALGAM COMPOSITE

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______________________________________________________________________________ Teacher Notes:

Monitor students closely to make sure that they have sufficient information on their paper during the Do Now to take back to their sub groups. Students who are struggling with getting started should be assisted during this time to get them motivated to be productive in group discussions.

Teacher should not say any to funnel students’ thinking during the Do Now and during the twenty minute literature review. The twenty minute literature review time should be closely timed.

Teacher should briefly explain the following. . . 1. Each student must state a fact about the filler they are defending. 2. Then the debate will begin with three points from each group which will be debated

by a representative from each group. 3. Summarize and conclude.

If the following points are not brought up during the debate, they should be discussed to close the activity.

• Polymerization forces composites to shrink o Unreacted double bonds cause post shrinkage.

• Certain composite resins hydrogen bond • Amalgam fillers are not bonded to the tooth • Corrosion occurs with the amalgam filler called (creep)

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DAILY LEARNING LOG

Prior Knowledge: The prior knowledge I had to bring into this lesson was…

MAIN IDEA: Today I learned…

3 Important Points about what I learned are: 1. 2. 3. x. x.

Societal Relevance: One way I could see how this information applies to the “real world” is …

Clarification: Some further questions I have about this topic are: (“How do you do it?” or “Can you teach it again?” Or any variation is not acceptable.)

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This page is intentionally left blank. This page should be trashed when this

document is printed.

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Initial Question Amalgam is used as a filler for teeth decay. Today more and more dentists are taking their practices to be amalgam free and are using composite fillings. As a young adult which type of filling would you have your dentist use?

Existing Information • I have some in my mouth • General knowledge of amalgam. • Teeth are made of calcium. • How cavities are formed. • Experience of dentist’s office.

Reflect and Organize Polymerization (initiation, propagation, termination) Hydrogen bonding

Which type of filling would you prefer?

Model Accepted?

Peer Review There is substantial information that supports both amalgam and composite fillings. The major differences are personal preferences & cost We have used amalgam as a filler for many years and not many people have had been exposed to Hg poisoning . Composite fillings are not as durable. Composite fillings cost too much and amalgam fillings are cheaper. Is light curing process of composite fillings dangerous to us?

Results Dentist are the practicing in amalgam free offices to prevent Hg poisoning which is why they are supporting composite fillings. Price is a major factor in which filling patients get. The composite fillings are prepared to match the color of an individual’s teeth.

New Information Needed • Introduction of amalgam and

composite fillings (Thesis). • How do composite fillings

work? • How do amalgam fillings work? • Are there any side effects

caused by both types of fillings? Community Knowledge There is a slight risk of getting Hg poisoning if the root of the tooth is exposed to amalgam fillings. Dentists are at risk of small amounts of Hg poisoning each time they use amalgam as a filler. Effects can be detrimental over a long period of time. Although composite fillings are expensive & do not withstand as long as amalgam fillings they are safer for both the patient and dentist.

Created by Vishal Patel